What does 'pathogen-free' status mean in mouse colonies?

• A. Absence of all pathogens.
• B. Absence of certain defined pathogens in the colony as determined by health surveillance.
• C. Pathogen-free means no bacteria at all.
• D. Freedom from any viruses.

Answer: (B)

Pathogen-free status means a colony has been tested and found to be free of a defined set of pathogens as determined by health surveillance. Laboratories specify a panel of agents (viruses, bacteria, parasites) that are known to impact mouse health or experimental results. If tests show none of those defined pathogens are present, the colony is considered free of them. This does not imply there are no microorganisms at all, nor that all bacteria or all viruses are gone. It simply means the particular pathogens on the surveillance panel are not detected. Nonlisted pathogens may still be present, and the status can change if a new pathogen is introduced or if the panel is updated.